Method for promoting the flow of molten materials into a mold using ultrasonic energy via probe means



Aug.19,1969 a. HOFFMAN ETAL 3,461,942

METHOD-FOR PROMOTING THE FLOW OF MQLTEN- MATERIALS INTO A MOLD USINGULTRASONIC ENERGY VIA PRO Filed Dec. 6, 1966 BE MEANS F/6.3 M M UnitedStates Patent US. Cl. 164-49 5 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to a method of casting metals comprising the steps ofheating metallic material to a liquid state, promoting metallic flow ofthe molten metallic material into a mold with ultrasonic vibrationsapplied to sprue'material by directly contacting an ultrasonic probetherewith, and simultaneously heating the mold and further heating themetallic material from an external source while subjecting the metallicmaterial to ultrasonic vibrations.

The present invention relates to the art of casting metals, and moreparticularly to methods and apparatus for the ultrasonic casting andtreating of metallic matter such as gold, silver, platinum, etc. andalloys thereof using ultrasonic energy. This application is acontinuationin-part of the patent to Robert Hoffman, No. 3,338,294,filed October 20, 1964, and issued August 29, 1967 for Method of CastingMaterials in Layers.

In the past various procedures and methods have been devised and used inattempts to prevent incomplete casting, miscasting and to reduce gasporosity in metallic castings, and to insure dense castings whichcompletely fill the mold and eliminate voids inside the casting. Toaccomplish this purpose, molds have been devised which permit theapplication of pressure, or the inclusion of escape holes, or the use ofporous investment material to permit escape of entrapped gases or theuse of centrifugal forces to compact the denser metal. However, this hasbeen only partially successful because remote gas pockets are usually soentrapped that the gas cannot be liberated. No method of casting yetdevised permits the heat treatment of the casting to proceed within themold while simultaneously acting to remove gas inclusion and render thecasting more dense, while also promoting flow within the mold cavity.

Accordingly, it is an object of the invention to provide a method andapparatus for making dental castings, jewelry and other precisioncastings, which will to a higher degree eliminate gas pockets in thecasting and reduce gas porosity, while also serving to increase thedensity of the castings and substantially increase the strength of thecastings.

A further object of the invention is to provide for better appearingcastings of measurably better physical characteristics by not onlysubjecting the castings to a suitably prolonged heat treatment asnecessary, but also vibrating the smelt at ultrasonic frequencies so asto compact and densify the casting, render the casting more homogeneous,increase the tensile and yield strength of the casting, conform thecasting more clearly to the contours of the mold in which the materialis being cast, and reduce gas porosity and improve grain structure.

An additional object of the invention is to provide aneasy method and asimple apparatus which will permit the successive casting in a singlemold of more than one metal while assuring diffusion and cohesivebonding of 'ice the successive diverse layers of metallic material to anextent heretofore not possible to be achieved.

A yet further object of this invention resides in the provision of anapparatus for facilitating the casting of metals in layers in a mannerso that the diiferent metals used in the different layers diffuse witheach other at the junction of the layers so as to provide for cohesivebonding without substantial alloying or intermixing the respectivemetals.

The concept of this invention features an apparatus for the ultrasoniccasting of metals which includes mold means having a cavity forreceiving metallic material. The mold means may be in the form of aunitary body of a suitable investment material, or it may be desired touse complementary mold halves. An ultrasonic transducer capable ofimparting ultrasonic vibrations in the order of 20,000 cycles per secondor greater as best determined for the desired casting material and molddimensions is coupled to the mold means. Electrical heating means in theform of a heating coil or the like is removably disposed about the moldmeans. This heating coil may be used in connection with mold halves tohold the mold halves in an assembled position while imparting heat tothe mold and to the metallic material in the concavity above the spruehole. A probe vibrating at ultrasonic frequencies is introduced into themelt, causing molecular movement, reducing surface tension and drivingthe molten metal into the mold, entirely filling every conformation ofthe mold cavity. The ultrasonic energy is applied outside the mold caseuntil solidification, but its radiation passes through the sprue toimprove the grain structure and reduce porosity and gas inclusions.

Another of the features of the invention is the concept of providingheating means for simultaneous operation with ultrasonic vibratorymeans.

Another feature of the invention resides in the concept of using thesame heating means for heating the mold and the metallic material tohold the mold in an assembled condition.

A further object of this invention is to promote flow of complexmaterials containing metal and ceramic particles, or just ceramicparticles. These particles, when part of an appropriate vehicle, arecast into the mold with ultrasonic vibrations. The subsequent heattreatment results in binding the cast particles.

Still further objects and features of this invention reside in theprovision of a method and apparatus for casting metals including theconcept of casting different metals in layers which is simple to employ,efiicient in operation, and especially adapted for uses in jewelryfoundings, jewelry manufacture, dentistry, and for making other similarprecision castings.

These, together with the various ancillary objects and features of theinvention which will become apparent as the following descriptionproceeds, are attained by this method and apparatus for ultrasoniccasting of metals. a preferred embodiment of the apparatus beingillustrated in the accompanying drawing, by way of example only,wherein:

FIG. 1 is a vertical sectional view illustrating details of constructionof an apparatus for casting metals constructed in accordance with theconcepts of the present invention;

FIG. 2 is a horizontal sectional view taken along line 22 in FIG. 1; and

FIG. 3 is a side elevational -view of the invention with probe removed.

With continuing references to the accompanying drawing, wherein likereference numerals designate similar parts throughout the various views,reference numeral 10 generally designates an apparatus constructed inaccordance with the concepts of the present invention for use in theultrasonic casting of metallic material. This apparatus includes a mold14. The mold 14 is provided with a cavity 24 surrounded by investmentmaterial 16 having vents 18 formed therein.

The mold 14 may b formed in any of the constructions set forth in theaforesaid patent No. 3,338,294 and include a mold cavity 24 terminatingin a sprue 26. The cavity 24 is of the shape of the desired casting, andthe material to be cast is placed into the cavity 28.

A spiral electrical heating ring 36 is disposed about the mold 14 andmay be held in place by tightening screw 38 or any other suitablefastening means. The heating coil may be connected through a suitableconventional electric plug. The precise controls and electrical heatingconnections for the electric heating coil 36 are optional. It is withinthe concept of the invention to employ other heating means as desired.

The heating coil 3-6 is preferably in the form of suitable bands of ironor steel preferably arranged in a spiral connection and fitting tightlyabout the mold 14.

In order to retain applied heat on the mold, a removable or hinged cover72 is disposed on the mold 14. This cover may be provided with suitableelectrical heating elements 74. The cover is provided with an opening 76therein for entry of a vibrating probe 80 connected to a transducer 82.The transducer is preferably a magnetostrictive transducer capable ofimparting vibrations in the order of 20,000 cycles per second on theprobe 80.

Procedures have been devised for utilizing this apparatus to provide forhigh density castings of a predetermined metallic material wherein thecasting quality is substantially improved and in which the gas porosityis substantially reduced. In carrying out these procedures, the materialbeing used is raised above its melting point in cavity 28 of theapparatus 10. Simultaneously, the transducer is actuated and the probe80 is inserted through opening 76 subjecting the metallic material tovibrations in the order of 20,000 to 25,000 cycles per second. Anexample of a silver casting of increased tensile strength and increasedyield point and a fine quality is as follows:

EXAMPLE I After the apparatus has been arranged, a suitable amount ofsilver to form the casting was heated approximately above its meltingpoint of 960.5 C. At the same time, the heating coils were excited untiltheir external temperature was measured at 1000 C. Simultaneously, thetransducer was excited causing ultrasonic vibrations to be applied tothe probe at 22,000 cycles per second. The casting was subjected to suchheat and vibrations for a period of one and one-half minutes, afterwhich time the heat in the coil was removed. A high quality casting ofreduced gas porosity was obtained.

It has been found that this apparatus may be employed in a novel methodof casting different material in layers. The new method is especiallyadapted for dental and jewelry castings and includes the concept ofseparately heating two or more differing metals to their liquid states.The first metal is first cast into the mold. The molten metal issimultaneously subjected to vibrations through use of the transducer andprobe 80 and to heat from an external source by actuating the heatingcoils. Then, a second material is cast in layer-like relation on top ofthe first metal. The molten metals are continuously subjected to theultrasonic vibrations through the probe 80 though the externaltemperature of the heating coil may be reduced. Then, a third layer ofanother metal is cast on top of the second metal with heat andvibrations still being simultaneously applied. This achieves a cohesivebonding of the various layers of metals Without substantial alloying o-rintermixing of the first and second metals, or of the second and thirdmetals.

An example of the foregoing method is as follows: i

4 EXAMPLE II Platinum is headed approximately 50 above its melting pointof 1773.5 C. While it is in the molten state, it is cast into the moldand vibrations on the order of 25,000 cycles per second are continuouslyapplied on the probe and the platinum material therein for a period ofone and one-half minutes. Heat is simultaneously applied from a sourceexternally of the mold by means of an electric heating coil having anexternal surface temperature of 1800 C. Approximately one minute ispermitted to elapse and the amount of current in the heating coil isreduced so that its outside temperature will be then 1100 C. At thattime, gold which has been heated to approximately 1100 C. is then castto form a layer on top of the platinum with the transducer and probestill imparting vibrations in the order of 25,000 cycles per second.After two minutes, a layer of silver is then cast directly on the goldand the vibrations and heat are permitted to continue. A cohesivelybonded high quality casting of three metals in layers was achieved.

It is to be recognized that any suitable rheostat or potentiometer maybe used to control the amount of heat to the heating coil 36, theprecise control means being selected as desired.

The present invention may be used for casting ceramic material in a moldby "subjecting the material to ultrasonic vibrations, and thereafterfusing the casting by application of heat through use of the heatingcoils.

The present invention permits the production of castings of combinationsof metals and ceramics and the like in one unit at one time.

A latitude of modification, substitution and change is intended in theforegoing disclosure, and in some instances, some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the present invention.

We claim:

1. A method of casting metals comprising the steps of heating metallicmaterial to a liquid state, promoting metallic flow with ultrasonicvibrations transmitted to said metallic material in its liquid state ina mold by applying said ultrasonic vibrations directly to a layer ofsaid metallic material in a liquid state located above said mold andcontinuously driving said metallic material while in a liquid state intoa mold, and simultaneously heating said mold and further heating saidmetallic material from an external source while subjecting said metallicmaterial to ultrasonic vibrations.

2. A method of casting different materials in layers comprising thesteps of separately heating a first material and a second material totheir liquid states, driving the first material While in a liquid stateinto a mold, simultaneously heating said mold and further supplying heatto said first material from an external source while transmitting tosaid first material in its liquid state ultrasonic vibraions of constantfrequency by direct contact between an ultrasonic probe and a layer ofsaid first metallic material in its liquid state located above said moldand then driving the second material while in a liquid state into themold on top of said first material while simultaneously further applyingheat on said mold and said first and second materials from an externalsource and transmitting ultrasonic vibrations to both of said materialsby directly contacting an ultrasonic probe with a layer of said secondmaterial in its liquid state located above said mold to patrial-lydiffuse said first and second materials to provide for a cohesivebonding Without substantial alloying of major amounts of said first andsecond materials.

3. A method of casting according to claim 2, wherein said first materialis gold and said second material is silver.

Referenccs Cited UNITED STATES PATENTS Hoke 164303 X Ornitz 16449 Thomas16495 X Hoffman 164-338 X 6 FOREIGN PATENTS 629,004 10/ 1961 Canada.591,552 1/1934 Germany. 479,993 2/1938 Great Britain.

OTHER REFERENCES Metal Progress, January 1961, TS300.M587, pp. 79-83.

J. SPENCER OVERHOLSER, Primary Examiner 10 R. SPENCER ANNEAR, AssistantExaminer US. Cl. X.R.

